Processes to separate hydrocarbon mixtures into component portions are an important necessity in industry and can employ a wide variety of techniques. Some separation processes involve contacting the hydrocarbon mixture with a membrane through which one component type is able to permeate. For example, U.S. Pat. No. 5,039,422 disclosed using a urea polymer chain extender with a compatible second prepolymer membrane to separate aromatic hydrocarbons from a mixture of aromatic and non-aromatic hydrocarbons. Other separation processes involve solvent extraction such as using 1,1-dioxide to recover high purity aromatic hydrocarbons such as benzene, toluene, and xylenes from hydrocarbon mixtures, see Wheeler, T. In Handbook of Petroleum Refining Processes; Meyers, R. A., Ed.; McGraw-Hill Book Company: New York, 1986, Chapter 8.4. A third type of separation process includes using a solid adsorbent to selectively adsorb desired components from the mixture. The components are later desorbed and recovered; see U.S. Pat. No. 4,048,111.
The separation of mixtures of hydrocarbons according to whether components are aliphatic or aromatic, and separations of the aliphatic hydrocarbons according to whether components are saturated or unsaturated are examples of separation processes that may be carried out using a solid adsorbent. The term aliphatic means those compounds which are not aromatic. Typically the solid adsorbents used in industry are zeolites or molecular sieve materials such as those described in U.S. Pat. No. 4,036,744 and U.S. Pat. No. 4,048,111. The present invention expands the range of useful solid adsorbents to effect hydrocarbon separations to include aryl-bridged polysilsesquioxanes. Specific aryl-bridged polysilsesquioxane materials and their preparation have been disclosed in Shea, K. J., and Loy, D. A. Chemistry of Materials 1989; Shea, K. J., Loy, D. A., and Webster, O. J. Am. Chem. Sec. 1992, pp. 6700-6710; Shea, K. J., Loy, D. A., Webster, O. Mater. Res. Soc. Symp. Proc. Vol 180 Better Ceram. Chem 1990, pp. 975-980; Shea, K. J., Loy, D. A., and Webster O. Polym. Mater. Sci. Eng. Vol 63 1990, pp. 281-285. This art teaches that organic groups can be introduced at regular intervals in an inorganic silicate framework, thus forming a three-dimensional organic-inorganic hybrid silicate-like polymeric material, also called an organically-bridged polysilsesquioxane. A two-dimensional representation of the well-known inorganic silicate framework is shown in I, and an analogous representation of the organically-bridged polysilsesquioxane where the 1 represents the organic group is shown in II. Of course, frameworks I and II, in reality, extend to form a three-dimensional, continuous, amorphous solid. ##STR1##
The specific organic bridging groups disclosed in the art include phenylene, diphenylene, terphenylene, and anthrylene. Organically-bridged polysilsesquioxanes containing these bridging groups are termed aryl-bridged polysilsesquioxanes. One stated objective of the disclosed work was to provide molecular level control of the morphology of the framework, another was to provide a new chromatographic support, and a third was use in optical applications. However, applicant has found that these materials perform as adsorbents for saturated, unsaturated aliphatic, and aromatic hydrocarbons at low temperatures. Furthermore, applicant has discovered that adsorbed saturated, unsaturated aliphatic, and aromatic hydrocarbons may be desorbed from the aryl-bridged polysilsesquioxanes using environmentally preferred saturated hydrocarbon desorbents.